This invention relates to a plasma sterilization indicator.
The various equipment and ware used in hospitals, laboratories, etc. are sterilized for disinfection. As techniques of such sterilization, steam sterilization, ethylene oxide gas sterilization and plasma sterilization, among others, are known. Among these techniques, the plasma sterilization technique comprises sterilizing a sterilizing load by means of a low-temperature plasma generated in an oxidizing gas atmosphere such as vaporized hydrogen peroxide and, as such, has the advantage that the required sterility can be attained at a comparatively low temperature.
The plasma sterilization technique, just as the other techniques, requires the provision of an indicator for verifying the sterility of a lot. Thus, an indicator for detecting the sterilizing gas concentration and exposure time must be provided in the plasma sterilization system.
As the prior art relevant to such an indicator, there is known a system for monitoring a course of low-temperature gas plasma sterilization involving an atmosphere composed predominantly of peracetic acid and acetic acid, for instance, wherein an indicator utilizing bromophenol blue, a pH indicator, is used to detect the sterility of a lot by taking advantage of the change in color from brilliant blue to light yellow owing to the activity of peracetic acid or acetic acid (U.S. Pat. No. 5,482,684).
However, the above indicator tends to reassume the initial color (the color before color change) if left standing for some time after the color change indicative of sterility and, therefore, has a drawback in terms of the steadiness of indication after color change. Once the indicator has reassumed the initial color, there is no telling any longer whether the sterilizing load in the system has successfully gone through sterilization.
It is, therefore, a primary object of the invention to provide a plasma sterilization indicator with which the end-point of plasma sterilization can be more accurately ascertained. The inventor of this invention did much research to overcome the foregoing drawback of the prior art and found that the above object can be accomplished by using a herein-defined ink composition in a plasma sterilization atmosphere. This invention is grounded on the above finding.
This invention, therefore, relates to the following plasma sterilization indicators.
1. A plasma sterilization indicator comprising a support and, as formed thereon, a color-change layer comprised of a variable color ink composition containing an anthraquinone dye having at least one amino group selected from the group consisting of a primary amino group and a secondary amino group.
2. The plasma sterilization indicator set forth in the above paragraph 1 which further comprises a non-color-change layer which does not change color in a plasma sterilization atmosphere as formed on said support and/or on said color-change layer.
3. The plasma sterilization indicator set forth in the above paragraph 1 wherein the variable color ink composition further contains a cationic surfactant of the quaternary ammonium salt type.
4. The plasma sterilization indicator set forth in the above paragraph 3 wherein the cationic surfactant of the quaternary ammonium salt type is an alkyl trimethylammonium salt.
5. The plasma sterilization indicator set forth in the above paragraph 1 which further comprises an extender and/or a resinous binder.
6. A method of detecting the sterility of a plasma-sterilizing load which comprises disposing the indicator defined in the above paragraph 1 in a plasma sterilization atmosphere and checking to see a change in color of said color-change layer.